1. Field of the Invention
The present invention relates to a method for fabricating an organic electroluminescent display and a fabrication apparatus used in the method.
2. Description of the Related Art
Organic electroluminescent displays (which will be hereafter occasionally referred to as “organic EL displays”) can be operated at a low driving voltage and have an excellent fast-response property. Moreover, organic electroluminescent displays are self-luminous displays and have a wide viewing angle. Therefore, organic electroluminescent displays are largely expected to be a next generation flat panel display and there has been increased development for various kinds of organic EL displays and fabrication methods which allow mass production for organic EL displays.
An organic EL display includes an organic electroluminescent layer (which will be occasionally referred to as an “organic EL layer”) having a single-layer or multi-layer structure including at least an organic electroluminescent light emitting layer (which will be hereafter occasionally referred to as an “organic EL light emitting layer”), a cathode, and an anode for holding the organic EL layer therebetween. The cathode injects electrons into the organic EL light emitting layer and the anode injects holes (positive holes) into the organic EL light emitting layer. In the organic EL light emitting layer, electrons and holes injected by the cathode and the anode, respectively, recombine to form excitons. Then, when the formed excitons are devitalized, light is emitted from the organic EL light emitting layer. Utilizing this light emission, the organic EL display displays letters, images, and the like.
Such organic EL displays are largely divided into two kinds depending on the type of the organic EL layer. Specifically, they are largely divided into two types of the organic EL layers, i.e., high molecular organic EL displays including an organic EL layer containing a high molecular organic electroluminescent material (which will be hereafter occasionally referred to as a “high molecular organic EL material”) and low molecular organic EL displays including an EL layer containing a low molecular organic electroluminescent material. In the case of a low molecular organic EL display, the organic EL layer is normally formed by a dry method such as vapor deposition or the like. On the other hand, in the case of a high molecular organic EL display, the organic EL layer is formed by wet processing such as print processing, an inkjet method (see e.g., Japanese Laid-Open Publication No. 10-12377 (Patent Reference 1) and U.S. Pat. No. 6,863,961 (Patent Reference 2), or the like).
In general, the organic EL material contained in the organic EL layer has a characteristic that it deteriorates very easily in an ambient atmosphere. Therefore, when the organic EL layer is formed in the ambient atmosphere, the organic EL material deteriorates in process steps for forming the organic EL layer, thus resulting in the problem in which innate characteristics of the organic EL layer cannot be achieved. Note that “characteristics of the organic EL layer” mean luminous brightness, luminous efficiency, brightness half-life, luminous life, and the like of the organic EL layer.
In view of the above-described problems, various techniques for controlling the fabrication atmosphere used in the process steps for forming the organic EL display including the process step of forming the organic EL layer have been disclosed. For example, in Japanese Laid-Open Publication No. 10-241858 (Patent Reference 3), a technique is disclosed including the process step of transferring an organic electroluminescent lamination structure formed in the process step of forming an organic electroluminescent lamination structure so that the organic electroluminescent lamination structure is not exposed to the atmosphere up to the process step of providing a shield member in vacuum or an inert gas atmosphere having a water content of 100 ppm or less.
In Japanese Laid-Open Publication No. 2003-77655 (Patent Reference 4), a technique is disclosed characterized in that process steps from an initial process step of forming an organic layer to the process step of forming a sealing portion are performed in an atmosphere (having a water concentration of 0.21 mg/l or less) of which a water volume is limited. Also, in U.S. Patent Application Publication No. 2003/175414 (Patent Reference 5), a technique is disclosed in which the process step of discharging a luminous function material is performed in an inert gas atmosphere (having a moisture concentration of 10 ppm or less).
Using techniques described in Patent References 3 through 5, deterioration of the high molecular organic EL material in the process step of forming the organic EL layer can be minimized. Thus, an organic EL display having excellent properties can be fabricated.
However, as in the methods disclosed in Patent References 3 through 5, when the organic EL layer is formed in an atmosphere in which oxygen and water are not substantially contained, for example, in a vacuum atmosphere and an inert gas atmosphere, the process step of forming the organic EL layer needs to be performed in a closed space such as a globe box and the like. In experimental and trial stages of production, the organic EL layer can be formed in a globe box, but in a mass production process step, it is difficult to form the organic EL layer in a globe box in terms of production costs.